1. Field of the Invention
The invention relates to a speed detecting device for a direct current motor, and to an electric fan with a motor speed detecting device.
2. Description of the Related Art
At present, an electric fan is used in electrical instruments and equipment, such as computers, for dissipating heat to ensure a normal operation thereof. Since a motor of the electric fan deteriorates after being in use for a period of time, the heat dissipating efficiency is reduced and can cause damage to electrical instruments and equipment. Therefore, it is necessary to detect the motor speed of the electric fan. Optical coupled and magnetic field detection techniques are two conventional techniques for speed detection of a direct current motor. The drawbacks of those techniques reside in that the motor must be redesigned and that the components for accomplishing speed detection are relatively expensive.